Nevirapine is already widely used to protect babies at birth. A single dose given to the mother as she goes into labor and to the baby at birth cuts transmission by 47 percent.
Researchers wanted to see if they could safely continue giving the drug to babies for as long as six weeks.
They gave 2,000 new babies either nevirapine or a vitamin solution between 2001 and 2007. At 6 months of age, the risk of postnatal HIV infection or death in infants who received the six-week regimen was almost one-third less than the risk for infants given only a single dose.
In many developing countries breast-feeding is the only option.
Nevirapine is sold under the brand name Viramune by privately held Boehringer Ingelheim.